Heaps are tables without a clustered index. These are generally to be avoided as reindexing is unable to reclaim lost space within them, thus the data remains fragmented and physical space is wasted.
The common recommendation to fix this is to add a clustered index, reindex the table then remove the clustered index. I would suggest the clustered index is left in place unless you have a good reason not to use one.
Another option is to move them to another database, or delete them altogether - if they are simply backups/dumps of other active tables.

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Although most have been tested working successfully, ensure you make backups before using them.
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